Bacteriophage Mu integrates via an unusual recombination system which recognizes specific attachment sites on the phage chromosome and recombines them with an apparently random sequence on the host chromosome. Our goal is to elucidate this integration mechanism. We plan to isolate integration deficient mutants of Mu using techniques which will allow the isolation of both plaque-forming and conditional lethal types of mutants Their defectiveness will be characterized using assays for lysogenization, integration, and excision. They will be tested for their ablity to be complemented for integration by int+ and int- phages, and the prophage content and structure of the complemented lysogens will be analyzed. The effect of the mutations on total DNA synthesis and various phage specific DNA forms will be determined. We will also continue a gentic and biochemical analysis of the host deletions associated with some integrated Mu prophages in an attempt to learn more about this type of Mu-induced mutation, its relation to normal Mu integration, and the factors which affect both types of integration. BIBLIOGRAPHIC REFERENCE; Howe, M. and E. G. Bade. Molecular Biology of Bacteriophage Mu. Science 190, 624-632, 1975.